Radar level gauges (RLGs) are suitably used for making non-contact measurements of the level of products such as process fluids, granular compounds and other materials contained in a tank. An example of such a radar level gauge can include a transceiver for transmitting and receiving electromagnetic waves, an antenna arranged to direct electromagnetic waves towards the surface and to return electromagnetic waves reflected by the surface to the transceiver, and processing circuitry adapted to determine the filling level based on a relation between electromagnetic waves transmitted and received by the transceiver.
In some applications, e.g. level detection of solids, such as grain, very high sensitivity is required due to the weak reflection from the surface. Also other factors, such as interference and impurities on the antenna affect the signal strength and thus the sensitivity requirements.
In such situations, it becomes relevant to reduce the coupling between the transmit channel and the receive channel, and to reduce leakage of electromagnetic energy from the comparatively strong transmit signal into the comparatively weak echo signal which may take in the antenna.
A solution to increase sensitivity would therefore be to use separate antennas for the transmit channel and the reception channel. If the electrical coupling between antennas are at least −50 dB, the sensitivity of such a system may be increased to 40-50 dB, compared to typical values of conventional systems of around 100 dB.
However, for practical reasons, it is not desirable to implement a two-antenna system in commercial RLG-systems. First of all there would be a significant cost increase, making such a system unattractive for the main market. Also, in many applications it is desirable to have as few openings in the tank as possible. Also for this reason, a two-antenna system is less attractive, at least if each antenna requires a separate opening in the tank wall.
Attempts have been made in the prior art to divide a single antenna into a transmitting portion and a receiving portion. For example, GB 1,105,503 discloses a parabolic antenna divided into two halves which are also separated from each other by a distance. However, existing prior art solutions have not been found adequate for use in radar level gauges.